1. Field of the Invention
The present invention generally relates to base station apparatuses, and more particularly to a base station apparatus in a radio communication system, which divides 1 cell into a plurality of sectors and communicates with a plurality of terminal stations according to Time Division Multiple Access (TDMA) via antennas provided for each of the sectors.
Recently, due to increasing number of terminal subscribers in mobile communication systems, there are demands to increase the number of terminal stations that can be accommodated by the base station. In order to efficiently increase the number of terminal stations that can be accommodated by the base station, it is necessary to not only effectively utilize the frequencies, but to also reduce the size and power consumption of the base station facility.
2. Description of the Related Art
FIG. 1 is a diagram showing the construction of a part of a conventional TDMA mobile communication system. The mobile communication system shown in FIG. 1 includes a mobile switching station 60 which connects to a public network and accommodates a plurality of base station apparatuses BS, a conventional base station apparatus 50 which is one of such base station apparatuses BS, directional antennas a1 through a3 which respectively cover communication areas of sectors 1 through 3, a cell (service area) 100 which is formed by the sectors 1 through 3, and mobile terminals A through G.
The conventional base station apparatus 50 fixedly allocates frequencies f1 through f3 to the sectors 1 through 3, respectively. In other words, the terminal A in the sector 1 uses the frequency f1, the terminals B and C in the sector 2 use the frequency f2, and the terminals D through F in the sector 3 use the frequency f3, in order to connect to the base station apparatus 50.
FIG. 2 is a timing chart for explaining a down-communication from the base station apparatus 50 to each of the terminals A through G. It is assumed that transmission slots T1 through T3 are used as speech channels for transmitting speech data, and a transmission slot T4 is used as a control channel for transmitting information related to a connection state of a terminal, connect request and the like. In this example, the terminal A in the sector 1 is accommodated in the time slot T1 of the frequency f1, the terminals B and C in the sector 2 are respectively accommodated in the time slots T1 and T2 of the frequency f2, and the terminals D through F in the sector 3 are respectively accommodated in the time slots T1 through T3 of the frequency f3. Hence, in 1 cell of the base station apparatus 50, a maximum of 3 terminals can be accommodated in each of the sectors 1 through 3 at the respective frequencies f1 through f3, and a total of 9 terminals can be accommodated simultaneously in 1 cell.
However, if an attempt is made in the above case to additionally accommodate a fourth terminal G in the sector 3, it is impossible to accommodate this terminal G in the sector 3 because there is no vacant time slot of the frequency f3 in the conventional base station apparatus 50.
In addition, if the terminal G is forcibly accommodated in the sector 3, it becomes necessary to increase the frequency used per sector. As a result, it is impossible to efficiently utilize the frequency, and there are problems in that the circuit scale, the power consumption and the cost of the base station apparatus all increase.
Accordingly, it is a general object of the present invention to provide a novel and useful base station apparatus in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a base station apparatus which can flexibly and efficiently accommodate a large number of terminals per sector.
Still another object of the present invention is to provide a base station apparatus is used for a radio communication system which divides one cell into a plurality of sectors and communicates with a plurality of terminal stations according to TDMA via antennas which are provided for each of the sectors. The base station apparatus includes a frequency-based distributor and modulator unit which distributes each of channel data to be transmitted in correspondence with each of time slots of a plurality of transmission frequency-based channels, and modulates the distributed channel data to modulated signals, a sector-based distributor and multiplexer unit which distributes the modulated signals to sector-based channels which are prescribed in advance in correspondence with the time slots, and multiplexes the distributed modulated signals for each of the sector-based channels, and a channel connection controller which generates distribution control information of each of the transmission frequency-based channels and the sector-based channels depending on a channel connect or disconnect request. According to the base station apparatus of the present invention, it is possible to flexibly and efficiently accommodate a large number of terminals for each sector, by use of a relatively simple construction. For this reason, it is possible, in a TDMA communication system, to effectively utilize the frequencies, enlarge the number of subscribers that can be accommodated, thereby improving the communication service and the service reliability.